Conventionally, the lithium ion battery (LIB) that is a storage battery used as a single cell has been low in voltage when used for industrial equipment and on-vehicle equipment.
For this reason, it has been required to form a battery pack by connecting many cells in series.
In order to respond to a demand for large electric power supply, a demand for higher capacity has been increasing in systems using a battery pack as a drive power supply or an auxiliary power supply for the purpose of higher performance and a longer available time.
Examples of a technique therefor include a battery pack device in which a battery pack is configured by connecting many batteries in series to configure battery groups and connecting the battery groups in parallel. In this case, in order to facilitate handling of batteries, a plurality of batteries may be connected in parallel and in series to be configured as a modularized storage battery device.
When a battery pack system is configured using a plurality of modularized storage battery devices, N-channel MOSFETs (a discharge control N-channel MOSFET and a charge control N-channel MOSFET) the drains of which are back-to-back connected (commonly connected) to a low potential side of a battery group included in each of the storage battery devices are provided to perform discharge control and charge control, and the battery groups included in the modularized storage battery devices are used by connecting them in series, the following problem may occur.
If the discharge control N-channel MOSFET that performs discharge control during discharging is turned off to be interrupted, for example, a reverse voltage is applied via a source terminal of the charge control N-channel MOSFET and a resistor for stabilizing the operation of the charge control N-channel MOSFET provided in between the source terminal and a gate terminal to an output terminal of an FET gate driver that drives the charge control N-channel MOSFET through a counter electromotive force, which may destroy the circuit of the FET gate driver.
If the charge control N-channel MOSFET that performs charge control during charging is turned off to be interrupted, an overvoltage caused by a counter electromotive force occurs, which may destroy a MOSFET control circuit.